Problem on Redeem code

Hello,

I have a list of VPP codes associated to an application, for download this application users must login and after that press the installation button. Once pressed this button is opened iTunes Store (past month App Store, now I don't know why is opening that) showing this overlay:

You have successfully redeemed your code.

Preparing to download....

And nothing happens, also application icon is not displayed into this overlay.

I tried this process at-least 5-6 times and the result is the same. Also adding the code manually nothing changes

The app is not into "Purchase" section of App Store and is not hidden. Even if the download is not starting, the code cannot be same code cannot be used again.

The url for reach the App Store/iTunes Store, from installation button is:

https://buy.itunes.apple.com/WebObjects/MZFinance.woa/wa/freeProductCodeWizard?c ode=.........